CN103630743B - The method of a kind of heterodyne system spectrum analyzer frequency correction - Google Patents

The method of a kind of heterodyne system spectrum analyzer frequency correction Download PDF

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CN103630743B
CN103630743B CN201310690052.1A CN201310690052A CN103630743B CN 103630743 B CN103630743 B CN 103630743B CN 201310690052 A CN201310690052 A CN 201310690052A CN 103630743 B CN103630743 B CN 103630743B
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frequency
signal
tuning
rbw
local oscillator
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CN103630743A (en
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罗光坤
郭连平
张勋
张波
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University of Electronic Science and Technology of China
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Abstract

The invention discloses the method for a kind of heterodyne system spectrum analyzer frequency correction, after processing, judge resolution bandwidth RBW when signal is sent to heterodyne system spectrum analyzer, if as RBW > 10 times of f mintime, being amplified signal by filter scan method or compress, envelope detection, video filtering process gets signal spectrum; As RBW≤10 times f mintime, by FFT scanning method, the error that the tuning frequency point value of record and the actual difference sending tuning frequency point value are converted into data point after FFT conversion is carried out spectrum error eliminating, thus improve identification frequency spectrum precision.

Description

The method of a kind of heterodyne system spectrum analyzer frequency correction
Technical field
The invention belongs to signal processing technology field, more specifically say, relate to the method for a kind of heterodyne system spectrum analyzer frequency correction.
Background technology
Spectrum analyzer can be divided into scan-type frequency spectrograph and non-scanning type frequency spectrograph according to principle of work, and scan-type frequency spectrograph mainly can be divided into filtering type and heterodyne system two kinds.Filtering type frequency spectrograph mainly adopts multi-channel filter frequency spectrograph, also referred to as parallel connection type wave filter, for different signal frequencies, different wave filters is adopted to process, last being transferred signals on screen by multitask scanner shows, but this frequency spectrograph structure needs to organize wave filter more, and resource consumption is many, and cost is higher.
Heterodyne system spectrum analyzer can realize carrying out multistage frequency conversion to high-frequency signal, and therefore sweep-frequency Békésy audiometer heterodyne frequency spectrograph can be analyzed by the signal very high to frequency, has resolution higher simultaneously, and measuring speed is fast, the advantages such as cost is lower, thus obtains widespread use.Due to the development of Digital Signal Processing in recent years, the processing speed of various digit chip is more and more faster, and resource is more and more abundanter, and price is more and more lower.The intermediate frequency process technology of frequency spectrograph progressively turns to digital intermediate frequency from analog intermediate frequency, and compared with traditional analog intermediate frequency, it is higher that digital intermediate frequency has stability, and cost is lower, is more conducive to the advantages such as scheduling and planning.
Heterodyne system frequency spectrograph obtains the essential information of required frequency by mixing, and obtains a frequency range by change local frequency, and scanning is exactly constantly update local frequency, makes a local oscillation signal just inswept frequency, reaches measurement object.Input signal is first through an attenuator, be on suitable level when ensureing signal input mixer, thus prevent overload, the distortion of gain compression and signal, signal by after attenuator through a low-pass filter, the Main Function of the low-pass filter in this place is: stop high-frequency signal to enter frequency mixer, prevent out-of-band-signal from producing unnecessary frequency response with the mixing of local oscillator phase at intermediate frequency, next, input signal and the signal phase mixing from local oscillator LO, signal after mixing is fallen in the passband of intermediate-frequency filter IF, this signal is by after wave filter, carry out the amplification or the compression that comprise signal, envelope detection, the process such as video filtering and display.Frequency sweep generator produces moving horizontally from left to right on screen, carries out tuning simultaneously, the change of local frequency is directly proportional to the ramp voltage of frequency sweep generator to local oscillator.
In frequency spectrograph, the digital medium-frequency signal that mixing obtains enters field programmable gate array (FPGA, Field-ProgrammableGateArray) after, first to its Digital Down Convert process, A-D converter (ADC, the baseband signal of the signal vanishing intermediate frequency AnalogtoDigitalConverter) exported, completes extraction simultaneously and falls digit rate operation.Baseband signal after down coversion, according to the difference of RBW, has two kinds of passage processing schemes: RBW > 10 times of f mintime, in FPGA, obtained the power spectrum of signal by detection algorithm, this method is called filter scan method; RBW≤10 times f mintime, deliver in digital signal processing (DSP, DigitalSignalProcessing) and carry out Fast Fourier Transform (FFT) (FFT, FastFourierTransformation) and converted analysis of spectrum, this method is called FFT scanning method, wherein f minfor the minimum tuning stepping that local oscillator LO tuning point can realize, therefore, RBW > 10 times of f minadopt traditional envelope detection, the process such as video filtering obtains the frequency spectrum of signal, and in RBW≤10 times f mintime, fft algorithm can be adopted to calculate the frequency spectrum of signal
But the limited precision of local oscillator LO tuning point, when frequency modulation step motion control word add 1 or subtract 1 time, the minimum tuning stepping f that LO tuning point can realize minfor:
Wherein, f reffor reference source stepping, N is local frequency frequency modulation precision, frequency modulation stepping is the least unit of front-end tunes frequency change, therefore the change of tuning frequency point is not arbitrary, can only change with the integral multiple of frequency modulation stepping, and the frequency between two humorous frequencies of neighboring tunable is irrealizable, can only quantize on the minimum tunable frequency of error, its error range is [-0.5f min, 0.5f min].Therefore, as resolution bandwidth RBW > 10 times of f of whole system mintime, be not very large on final testing result impact; Otherwise RBW≤10 times f minerror effect is just obvious.
Summary of the invention
The object of the invention is to overcome the deficiencies in the prior art, the method of a kind of heterodyne system spectrum analyzer frequency correction is provided, the error that the tuning frequency point value of record and the actual difference sending tuning frequency point value are converted into data point after FFT conversion is carried out spectrum error eliminating, thus improves frequency spectrum precision.
For achieving the above object, the method for a kind of heterodyne system spectrum analyzer of the present invention frequency correction, is characterized in that, comprise the following steps:
(1), radiofrequency signal is input to attenuator after, after low-pass filter filtering, be input to frequency mixer;
(2) signal, with reference to source produced is input to local oscillator LO, then the output signal of local oscillator LO is input to frequency mixer, when the frequency modulation step motion control word of local oscillator LO add 1 or subtract 1 time, the minimum tuning stepping f that described local oscillator LO tuning point can realize minfor: wherein, f reffor reference source stepping, N is local oscillator LO frequency frequency modulation precision; Frequency sweep generator produces moving horizontally from left to right on screen, carries out tuning simultaneously, the change of local oscillator LO frequency is directly proportional to the ramp voltage of frequency sweep generator to local oscillator LO;
(3), by the output signal of frequency mixer intermediate-frequency filter filtering is input to, if filtered signal resolution bandwidth RBW > is 10 times of f mintime, by filter scan method signal amplified or compress, envelope detection and video filtering process get signal spectrum; If filtered signal resolution bandwidth RBW≤10 times f mintime, by FFT scanning method, record actual required tuning frequency point value or desirable tuning frequency point value f ituning frequency point value f is sent with reality lOerror: Δ f=f lO-f i, wherein, actual transmission tuning frequency point value f lOwith minimum tuning stepping f minthere is following relation: f lO=Mf minm ∈ [1,2 n] ∩ Z, Z represents set of integers, again the error delta f obtained is converted into the error of the rear data point of FFT conversion, wherein, frequency interval in FFT transformation results between adjacent two frequencies is RBW/2, then the frequency shift (FS) that Δ f causes is 2 Δ f/RBW, finally according to Δ f be just or negative FFT is converted after frequency sequence to the right or be moved to the left round (2 Δ f/RBW) individual point, get signal spectrum, wherein immediate integer is got in round () expression.
Goal of the invention of the present invention is achieved in that
The method of heterodyne system spectrum analyzer frequency of the present invention correction, judges resolution bandwidth RBW when signal is sent to heterodyne system spectrum analyzer, if as RBW > 10 times of f after processing mintime, being amplified signal by filter scan method or compress, envelope detection, video filtering process gets signal spectrum; As RBW≤10 times f mintime, by FFT scanning method, the error that the tuning frequency point value of record and the actual difference sending tuning frequency point value are converted into data point after FFT conversion is carried out spectrum error eliminating, thus improve identification frequency spectrum precision.
Meanwhile, the method for heterodyne system spectrum analyzer frequency of the present invention correction also has following beneficial effect:
Heterodyne system spectrum analyzer adopts filter scan method and FFT scanning method two kinds of methods, the employing efficiency of signal can be improved, save the employing time, error simultaneously by the tuning frequency point value of record and the actual difference sending tuning frequency point value are converted into data point after FFT conversion in FFT scanning method carries out spectrum error eliminating, thus improves frequency spectrum precision.
Accompanying drawing explanation
Fig. 1 is the ultimate principle block diagram of heterodyne system spectrum analyzer frequency Correction Method of the present invention;
Fig. 2 is that the just front spectrogram of frequency repaiied by heterodyne system frequency spectrograph;
Fig. 3 is the revised spectrogram of heterodyne system frequency spectrograph frequency.
Embodiment
Below in conjunction with accompanying drawing, the specific embodiment of the present invention is described, so that those skilled in the art understands the present invention better.Requiring particular attention is that, in the following description, when perhaps the detailed description of known function and design can desalinate main contents of the present invention, these are described in and will be left in the basket here.
Embodiment
Fig. 1 is the ultimate principle block diagram of heterodyne system spectrum analyzer frequency Correction Method of the present invention.
In the present embodiment, reference source is for oscillator, as shown in Figure 1, input signal of the present invention is first through an attenuator, be on suitable level when ensureing signal input mixer, thus prevent overload, the distortion of gain compression and signal, signal by after attenuator through a low-pass filter, the Main Function of the low-pass filter in this place is: stop high-frequency signal to enter frequency mixer, prevent out-of-band-signal from producing unnecessary frequency response with the mixing of local oscillator phase at intermediate frequency, next, the signal that reference oscillator produces is input to local oscillator LO, again signal is input to frequency mixer, but the limited precision of local oscillator LO tuning point, when frequency modulation step motion control word add 1 or subtract 1 time, the minimum tuning stepping f that described local oscillator LO tuning point can realize minfor: wherein, f reffor reference oscillator stepping, N is local oscillator LO frequency frequency modulation precision, and frequency sweep generator produces moving horizontally from left to right on screen, carries out tuning simultaneously, the change of local oscillator LO frequency is directly proportional to the ramp voltage of frequency sweep generator to local oscillator LO, input signal and the signal phase mixing from local oscillator LO, the signal after mixing is fallen in the passband of intermediate-frequency filter IF, after this signal passes through wave filter, if signal resolution bandwidth RBW > is 10 times of f mintime, by filter scan method signal amplified or compress, envelope detection and video filtering process get signal spectrum, if signal resolution bandwidth RBW≤10 times f mintime, by FFT scanning method, record actual required tuning frequency point value or desirable tuning frequency point value f ituning frequency point value f is sent with reality lOerror: Δ f=f lO-f i, wherein, actual transmission tuning frequency point value f lOwith minimum tuning stepping f minthere is following relation: f lO=Mf minm ∈ [1,2 n] ∩ Z, Z represents set of integers, again the error delta f obtained is converted into the error of the rear data point of FFT conversion, wherein, frequency interval in FFT transformation results between adjacent two frequencies is RBW/2, then the frequency shift (FS) that Δ f causes is 2 Δ f/RBW, finally according to Δ f be just or negative FFT is converted after frequency sequence to the right or be moved to the left round (2 Δ f/RBW) individual point, get signal spectrum, wherein immediate integer is got in round () expression.
Fig. 2 is that the just front spectrogram of frequency repaiied by heterodyne system frequency spectrograph.
Fig. 3 is the revised spectrogram of heterodyne system frequency spectrograph frequency.
In the present embodiment, the stepping f of reference source oscillator ref=100MHz, local oscillator tuning precision is 24, then tuning stepping least unit f min=5.96Hz, tuning error scope is [-2.98Hz, 2.98Hz].In design, the RBW gear that FFT analysis of spectrum is corresponding comprises 30Hz, 10Hz, 3Hz and 1Hz, when RBW=3Hz, the deviation of the maximum generation of Δ f 2 frequencies, and when RBW=1Hz, the deviation of the maximum generation of Δ f 6 frequencies, therefore needs to revise FFT result, to eliminate radio-frequency (RF) local oscillator end tuning error.Suppose RBW=1Hz, error delta f=2.98Hz, frequency shift (FS) so caused by Δ f is counted and is approximately equal to 6, namely the deviation of 3Hz is mapped as 6 frequencies on frequency domain, when therefore compensating this deviation, the actual Frequency point that will get should along frequency axis toward moving left 6 points, and the spectrogram before and after frequency correction as shown in Figures 2 and 3.
Although be described the illustrative embodiment of the present invention above; so that those skilled in the art understand the present invention; but should be clear; the invention is not restricted to the scope of embodiment; to those skilled in the art; as long as various change to limit and in the spirit and scope of the present invention determined, these changes are apparent, and all innovation and creation utilizing the present invention to conceive are all at the row of protection in appended claim.

Claims (1)

1. a method for heterodyne system spectrum analyzer frequency correction, is characterized in that, comprise the following steps:
(1), radiofrequency signal is input to attenuator after, after low-pass filter filtering, be input to frequency mixer;
(2) signal, with reference to source produced is input to local oscillator LO, then the output signal of local oscillator LO is input to frequency mixer; When the frequency modulation step motion control word of local oscillator LO add 1 or subtract 1 time, the minimum tuning stepping f that described local oscillator LO tuning point can realize minfor: wherein, f reffor reference source stepping, N is local oscillator LO frequency frequency modulation precision, frequency sweep generator produce on screen from left to right move horizontally signal, and utilize this signal to carry out tuning to local oscillator LO, the change of local oscillator LO frequency be directly proportional to the ramp voltage of frequency sweep generator;
(3), by the output signal of frequency mixer intermediate-frequency filter filtering is input to, if filtered signal resolution bandwidth RBW > is 10 times of f mintime, by filter scan method signal amplified or compress, envelope detection and video filtering process get signal spectrum; If filtered signal resolution bandwidth RBW≤10 times f mintime, by FFT scanning method, record actual required tuning frequency point value or desirable tuning frequency point value and reality and send tuning frequency point value f lOerror: Δ f=f lO-f i, wherein, f irepresent actual required tuning frequency point value or desirable tuning frequency point value, actual transmission tuning frequency point value f lOwith minimum tuning stepping f minthere is following relation: f lO=Mf minm ∈ [1,2 n] ∩ Z, Z represents set of integers, again the error delta f obtained is converted into the error of the rear data point of FFT conversion, wherein, frequency interval in FFT transformation results between adjacent two frequencies is RBW/2, then the frequency shift (FS) that Δ f causes is 2 Δ f/RBW, finally according to Δ f be just or negative FFT is converted after frequency sequence to the right or be moved to the left round (2 Δ f/RBW) individual point, get signal spectrum, wherein immediate integer is got in round () expression.
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CN104316760B (en) * 2014-10-10 2017-07-11 中国电子科技集团公司第四十一研究所 A kind of dominant frequency signal determinating circuit and decision method for being applied to microwave frequency counter
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